Ejectors, sometimes called gas (e.g. steam) ejectors or venturi ejectors are well known. They may be used to maintain a vacuum or to compress a gas. The advantage of the ejector over conventional mechanical pumps such as piston pumps or compressors and diaphragm pumps is that it has no moving parts and is generally robust (subject to filtering the gas streams to reduce pitting and corrosion). Typically ejectors are subsonic, as supersonic ejectors tend to produce a low pressure exit stream. Additionally supersonic ejectors are sensitive to the design/construction parameters.
An ejector typically comprises an expansion nozzle port through which a motive gas enters the ejector through an inlet port. The gas is expanded to a lower pressure as it passes through a constricted throat section of the nozzle. Generally there is a suction port opening into an enclosed chamber about the expansion nozzle through which the gas to be captured is drawn into the ejector. Then downstream of the expander there is a diffuser section having an inlet, a throat section and a diverging discharge section.
Conventional subsonic ejectors are commonly used to maintain a vacuum on a system such as disclosed in the following patents.
U.S. Pat. No. 5,380,822 issued Jan. 10, 1995 discloses the use of a gas, typically steam, ejector to maintain a lower pressure in the later stages of a falling strand devolatilizer than in the down stream condenser to prevent water from freezing. This patent doesn't teach supersonic ejectors nor does it suggest ejectors could be used in sequence or in tandem.
U.S. Pat. No. 6,855,248 Issued Feb. 15, 2005 to Oliver et al. assigned to Sulzer Chemtech Limited teaches the use of a steam ejector to maintain a vacuum on a processing column (example 1). The patent does not teach the use of a gas ejector to recycle off gases. Further the patent does not teach tandem supersonic ejectors.
U.S. Pat. No. 6,330,821 issued Dec. 18, 2001 to Arnold et al. assigned to The Goodyear Tire & Rubber Company teaches the use of a gas ejector to maintain a vacuum on a part being tested. The patent does not teach the use of a gas ejector to recycle off gases. Further the patent does not teach tandem supersonic ejectors.
U.S. Pat. No. 4,194,924 issued Mar. 25, 1898 assigned to The United States of America as represented by the Secretary of the Air teaches distilling a carrier solvent and JP-4 in a heated vacuum column in which the vacuum is provided by a gas (steam) ejector. The patent does not teach the use of a gas ejector to recycle off gases. Further the patent does not teach tandem supersonic ejectors.
U.S. Pat. No. 4,834,343 issued May 30, 1989 to Boyles teaches a non flooded treatment column including a venturi device within the top of the column to redisperse the gas beneath the fluid level (FIG. 6 and Col. 7 lines 60 to 65). However, the patent does not teach supersonic ejectors nor does it teach tandem ejectors or venturi's. Further the patent does not teach off gases which have escaped a containment zone such as a seal.
The present invention seeks to provide a simple and economical process to capture off gases and recompress them to be used at a higher pressure.